Mexican Cession

The Mexican Cession was a region of the American West that was signed over to the United States by Mexico under the 3 February 1848 Treaty of Guadalupe Hidalgo at the end of the Mexican-American War. California, Nevada, Utah, and parts of Arizona, New Mexico, Colorado, and Wyoming were ceded to the USA, some 529,000 square miles of land. The Gadsden Purchase of 1853 signed over the rest of Arizona to the United States. The cession would be admitted to the union as a package of free states under the Wilmot Proviso, angering pro-slavery activists in the American South; the cession was inadvertently one of the causes of the American Civil War.